FNB Authorized a Payment on a Cancelled Card

On the 13th of November, i received a notification that i did a purchase of R29 000. Transaction shows that it used a card that i cancelled in May 2021. To biggest shock, FNB tells me about filling a form with establishing sense of urgency in the matter. They are not able to explain how did they authorize a transaction that used a card that was cancelled in May 2021. The transaction description shows a POS (Point Of Sale) meaning i tapped or swiped the card on the 11th November. Transaction was done by Dollar Thrifty and FNB but both cannot explain to me what happened